Don't let the bad bugs bite

A dangerous monster is lurking, just waiting to make its next move, writes Alexandra Smith.

Forget a casual swat in the middle of the night to silence that irritating buzz near your ear.

It may be enough to do away with the garden variety mozzie that hovers around through summer's hot sleepless nights but it would take more than a light slap to kill this aggressive monster.

The Asian tiger mosquito is tough. So tough that if it was to beat Australia's border controls, not to mention our flyscreens, Sydney would face its first real dengue fever threat since World War II.

"The Asian tiger mosquito is an insect of medical importance and it would cause major dramas if it made its way in through one of the ports," says Stephen Doggett, a senior scientist at Westmead Hospital's medical entomology department.

The Asian tiger mosquito is a carrier of dengue fever, a virus with side-effects so painful that it is also known as breakbone fever and can be fatal. It produces symptoms such as limb pain, high fever, rash and severe headache and can be treated only with analgesics and plenty of fluids. Severe cases may require hospitalisation for intravenous fluids and supportive care.

In February, a Torres Strait Islander became the first Australian to die from the virus since a 1904 breakout in Brisbane, which killed 94 people.

Rates of the fever are increasing worldwide, with an estimated 5 million cases a year, according to the World Health Organisation. Indonesia is fighting its worst outbreak. More than 15,000 people in 22 of the country's provinces have been affected since January, and more than 260 people have died, according to Indonesian health ministry figures.

North Queensland is also on high alert as it battles a dengue outbreak. Last year there were seven outbreaks in the tropics affecting more than 600 people, 459 of them in Cairns.

Dengue fever is most often transmitted to humans through female aegypti mosquitoes, which acquire the virus while feeding on the blood of an infected person. But while the aegypti mosquito is responsible for almost all dengue cases, the Asian tiger mosquito poses a real threat to regions south of the Australian tropics.

The mosquito, which earned its name because of its ornamental striped colour patterns and its aggressive biting habits, would thrive in Sydney's mild climate, according to Doggett.

"The albopictus [Asian tiger] could withstand much colder temperatures than the aegypti and could no doubt spread far and wide in Australia," he says.

The mosquito has already invaded the United States, where the first wave hit Texas in 1985 after mosquitoes hatched from eggs believed to have been transported in recycled tyres from Asia. The species lays eggs in water containers such as flower pots, buckets, gutters and dog bowls, in a similar fashion to the aegypti.

Richard Russell, the medical director of the Westmead entomology department, says dengue fever was last detected in NSW in 1925, but it could return with the Asian tiger mosquito.

The aegypti mosquito did not make it as far south as Sydney in the 1920s but was found in Gosford before retreating to far north Queensland by the end of World War II.

"This is certainly a possibility and a worry and it only hasn't arrived because the Australian Quarantine Inspection Service is doing a very good job of keeping it out," Russell says.

The Asian tiger mosquito, which also carries yellow and Ross River fevers, was discovered in Sydney in 1999, reportedly via a Japanese ship carrying tyres. One mosquito was found in traps in Port Botany during routine quarantine surveillance.

Doggett says it would only take one pregnant female to establish itself in NSW. "If it did arrive, I am doubtful we could contain it and that would mean there would a real danger of dengue fever spreading in all states of Australia" he says. "There is certainly no doubt that it is something we are very worried about."